Research On Mechanism Of Crystallization And Opitimization Of Properties Of BSTS Polar Glass-Ceramics

In this paper, based on the original glass system BaO-SrO-TiO2-SiO2, the process and mechanism of crystallization were studied and this process was simulated by the computer. In the meantime, the optimal technical conditions of heat-treating and some properties of glass-ceramics were studied. By means of SEM and energy analyzer, the mechanism of crystallization of glass-ceramics was discussed. The research of microstructures shows that the growing process of grains can be described as follows. When the temperature arrives at 900℃, the oriented layers of crystallization begin to appear on the surfaces of the glasses. Then the oriented crystal grains grow perpendicular to the layers of crystallization. Ultimately, the polar glass-ceramics are formed. The crystallization process of glasses begins on the surface of glasses and grows directional to the interior of glasses one layer after another. And the direction of the oriented crystal grains is always perpendicular to the surface of the glass. After a time of heat preservation, the increasing of duration will be harmful to the properties of materials. The discussions and calculations of kinetics show that the activation energy of crystallization of the block and powder samples are separately 112.7and 102.8. And the difference of two values is due to the discrepancy of the areas of surfaces of the samples. In addition, the coefficient of velocity of crystal transformation, the radius of crystal and the percentage of crystal volume are calculated in this paper. Through the repeating experiments and the calculations of the ortho-trial tables, the optimal technical conditions of BSTS polar glass-ceramics was found and the crystallization temperature and the time of heat preservation were proved to be the most important aspects during the crystallization process of glass-ceramics. Some properties demonstrated that BSTS polar glass-ceramics is a promising material in the high temperature applications and can be used as an alternative substrate of SAW devices.